The present invention relates to seating units, and more particularly relates to a chair having a formed cushion, where the cushion is shaped to mate with a stiffener in a manner adapted to facilitate subassembly into an upholstery sock, and also shaped to optimize comfort and appearance in the final seating product. Further, the present invention concerns methods of assembly related to the above.
Many chairs include a back structure covered by an upholstery subassembly, where the upholstery subassembly forms a sock-like hollow covering that can be pulled onto the back structure to aesthetically cover all or part of the back structure. For example, see U.S. Pat. No. 6,425,637 Peterson. A common problem in many such chair designs is that the sock must be tight enough to eliminate unattractive wrinkles and to eliminate loose fabric sections on the upholstery, but must not be so tight as to prevent the sock from being slipped onto the back structure or to cause distortions to its cushion during assembly. Quality problems often occur during assembly due to normal manufacturing variations in stitching and variations in part dimensions and material properties such as elasticity, compressibility, and tensile strength. Also, traditional polyurethane foam cushion material tends to frictionally drag on the sock (or grip the back structure if it is part of the upholstery subassembly) during assembly. Each of these conditions can result in distortions and non-uniformities in the cushion and/or in the upholstery after assembly (e.g., wrinkles, distortions, puckers, loose fabric sections, irregular corners, etc.). It is often difficult to know whether the distortions and non-uniformities are caused by conditions prior to, during, or after assembly . . . or a combination thereof. The problems tend to be especially evident at corners and feature lines of the back where dimensional variations in mating components and stitch lines are easily seen. Depending on the chair design, distortions and non-uniformities can be very unsatisfactory to consumers (particularly in higher end chairs), since such distortions and non-uniformities are interpreted as low quality. Thus, an improvement is desired that facilitates construction of an upholstery subassembly, and that facilitates assembly of the upholstery subassembly to a back structure. Further, an improvement is desired that helps eliminate or at least control distortions and non-uniformities. It is believed that part of a solution to the present problems is connected to managing and distributing the tension and stress between the cushion and the upholstery sock, particularly at highly visible corners.
Loose unsupported sections of upholstery are particularly difficult to control in large flat or recessed areas where the upholstery is poorly supported or totally unsupported. For example, if the upholstery is not properly and uniformly tensioned in all directions, the material hangs loose and sags. But if the upholstery is unevenly tensioned, the material forms undulating ridges and stretch-related channels that extend parallel a direction of the “over-tension”. If the upholstery is simply too highly tensioned, the cushion may become locally distorted via uneven compression of the cushion, thus also causing visual defects. These conditions are especially problematic in large relatively-flat areas, such as along a front middle area of a chair back (i.e., a lumbar region) or on a center of a relatively flat-topped chair seat. Also, these conditions will occur when a concave face of a back support shell (i.e., a shallow depression surrounded by a ring of marginal material higher than a bottom of the shallow depression), since tension on the upholstery material will cause the upholstery material to bridge across the bottom at a location spaced above the bottom, . . . instead of pulling the upholstery against the bottom of the shallow depression. Typically, these problems may worsen over time and with use of the chair as the fabric stretches and as the cushion takes on a compression set.
It is noted that Peterson U.S. Pat. No. 6,425,637 discloses a chair construction of interest, including a PETE or PET cushion of non-woven fibers (see FIGS. 3-6 and 14), an upholstery sock-like structure of interest (see FIGS. 3-7 and column 6, lines 15+) and related assembly method (see FIGS. 3-7 and 13). However, improvement is desired so that the cushion holds itself on the cushion stiffener during assembly of the upholstery sock onto the cushion and cushion stiffener and to eliminate wrinkles and unevenly stretched areas after the assembly. Also, improvement is desired to better secure the cushion stiffener onto the back support shell.
Sometimes attempts are made to control the upholstery by adhering the upholstery to the cushion under the problem area. However, adhesives are expensive to purchase, and to apply . . . and further are not always a solution to the appearance problem. Further, adhesives can affect compression of the cushion and adversely affect user comfort. Still further, over time the cushion and upholstery may stretch and give, resulting in loose unsupported sections of upholstery.
One attractive style for chairs comprises a layered look where the upholstery subassembly (including a cushion) is attached only to a face of a support structure on a chair back or seat. In such chair designs, it is important to maintain proper centered placement of the upholstery subassembly on the support structure (i.e., to prevent the cushion and/or upholstery from creeping or “walking” toward one side or another of the support structure) to avoid warranty and appearance problems after significant use of the chair. Further, it is important that the attachment of the upholstery subassembly to the support structure be both secure, relatively thin, and preferably hidden, so that the style can be maintained without forcing the chair to have a thick heavy appearance, and without forcing the chair to include multiple visible screw heads or containment structure. Further, it is desirable to provide an attachment system that eliminates screws and time-consuming assembly steps, and that can be formed integrally with the underlying mating components.
Thus, a system having the aforementioned advantages and solving the aforementioned problems is desired.